JP3298971B2 - Polyester film for coating can material and method for producing the same - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a metal plate for forming a can body of a can body, for example, a welded can body material such as a surface-treated steel sheet, which is heated and bonded via a thermosetting resin-based adhesive to form a protective coating layer. The present invention relates to a polyester film to be formed and a method for producing the same.

[0002]

2. Description of the Related Art As a metal can body used for containers of beverages and the like, a can body is formed by welding and joining both side edges of a can body blank obtained by cutting a surface-treated steel sheet for a can into strips. There is known a welded can body in which a separately manufactured can lid is double-wrapped around both ends of the can body. In the welded can body, in order to avoid that the flavor of the content is changed due to corrosion of the base metal or the eluted metal component due to contact between the content and the surface-treated steel sheet for the can, which is the base metal, the inner side of the can. Is coated with a paint such as an epoxy-phenol resin, and the outer surface of the can is coated with a paint for imparting aesthetic appeal.

Conventionally, the above-mentioned welded can body has been manufactured by baking with a heating oven every time the coating is performed on the inner and outer surfaces of the surface-treated steel sheet for cans. In the manufacturing method, the working environment tends to be harmed by the heat of the heating oven and the volatile organic solvent. In particular, on the outer surface side where multicolor printing is performed, baking by the heating oven is performed every time coating of 2 to 4 colors is performed. Therefore, the above tendency becomes stronger.

Accordingly, studies have been made to form a protective coating layer by coating the inner and outer surfaces of the surface-treated steel sheet for cans with a polyester film. According to this configuration, the corrosion of the surface-treated steel sheet can be prevented on the inner surface of the can, and in the can body in which the inner surface protective coating is applied and baked on the inner surface of the can, the component slightly elutes from the coating film. The flavor of the changing contents can be protected. In addition, by coating with a printed polyester film on the outer surface side of the can, it is possible to impart aesthetics and perform a required display without depending on painting. Therefore, by coating the inner and outer surfaces of the surface-treated steel sheet for cans with a polyester film to form a protective coating layer, the painting and baking steps in the conventional production method are not required, and it is expected to improve the working environment.

In order to cover the inner and outer surfaces of the surface-treated steel sheet for a can with a polyester film, a method of bonding the polyester film to a heated metal by pressing is considered.

[0006] However, it is not possible to obtain a sufficient adhesive force to the conventionally used surface-treated steel sheet for cans by simply pressing the polyester film for a short time under heating. Also, in order to bond the polyester film to the surface-treated steel sheet for a can through a normal thermosetting resin-based adhesive, there is a disadvantage that long-time heating at a high temperature is required to obtain a sufficient adhesive force. is there.

[0007]

SUMMARY OF THE INVENTION Accordingly, the present invention has been made to solve the above-mentioned problems, and it is possible to sufficiently heat a can body and a metal plate for forming a can body by heating at a high temperature for a short time. It is an object of the present invention to provide a polyester film for covering a can body material capable of obtaining a strong adhesive force and a method for producing the same.

Further, the present invention provides a polyester film capable of sharpening the printing on a can body formed from the metal plate when the polyester film is printed, and a method for producing the same. The purpose is to:

[0009]

In order to achieve the above object, a polyester film for covering a can body material according to the present invention comprises:
A polyester film that is heat-bonded to a metal plate for forming a can body of a can body via a thermosetting resin-based adhesive to form a protective coating layer, and has a number average molecular weight of 5,000 to 20,000 on one surface of the polyester film. Characterized in that an adhesive layer made of a resin containing the epoxy resin and the acid anhydride-based curing agent in a weight ratio of 70/30 to 99/1 is provided.

The epoxy resin has a number average molecular weight of 500.
When it is less than 0, the adhesive strength is insufficient, and when it exceeds 20,000, the viscosity becomes high and the coating workability is inferior. When the number average molecular weight is less than 5,000, the adhesiveness of the adhesive layer is increased and the tack-free property is reduced when the adhesive layer is formed by previously applying and drying the polyester film.

In the adhesive layer, the amount of the acid anhydride-based curing agent is 1 to 99 parts by weight of the epoxy resin.
If the amount is less than 10 parts by weight, it takes a long time to cure the epoxy resin even when heated at a high temperature, and even if the compounding amount of the acid anhydride curing agent is more than 30 parts by weight with respect to 70 parts by weight of the epoxy resin The effect of accelerating the curing of the epoxy resin is not further improved.

The acid anhydride-based curing agents include pyromellitic anhydride, benzophenonetetracarboxylic anhydride,
Examples thereof include phthalic anhydride, tetrahydrophthalic anhydride, methylcyclohexanedicarboxylic anhydride, trimellitic anhydride and derivatives thereof, and are excellent in curability, blocking resistance of a film after coating, tack-free property and the like. Therefore, trimellitic anhydride-based curing agents comprising trimellitic anhydride and its derivatives are suitable. Examples of the derivative of trimellitic anhydride include glycerol tristrimellitate anhydride, a dimer of trimellitic anhydride, and ethylene glycol bistrimellitate anhydride.

The epoxy resin forming the adhesive layer is as follows:
It is preferably a bisphenol-type epoxy resin obtained by a reaction between bisphenol and epichlorohydrin, and may further contain another curing agent such as a phenol resin in addition to the acid anhydride-based curing agent.

[0014] The polyester film is excellent in suitability for contents such as strength, transparency and flavor retention, and any polyester can be obtained by polycondensation of a dicarboxylic acid component and a diol component. May be a polyester obtained by polycondensation of an aromatic dicarboxylic acid such as naphthalenedicarboxylic acid, terephthalic acid, or isophthalic acid, and a diol such as ethylene glycol, propylene glycol, or butylene glycol. Particularly preferred is a polyester obtained by polycondensation of naphthalenedicarboxylic acid and ethylene glycol (polyethylene naphthalate) or a polyester obtained by polycondensation of terephthalic acid and ethylene glycol (polyethylene terephthalate).

The polyester may contain another dicarboxylic acid component or diol component in the dicarboxylic acid component or diol component, if desired. Other preferable polyesters other than polyethylene terephthalate include JP-A-51-42786 and JP-A-64-70.
And polyesters described in JP-A No. 352 and JP-A-2-242738.

It is preferable that the surface of the polyester film to which the adhesive is applied is previously subjected to a surface oxidation treatment such as corona discharge in order to improve the adhesive strength.

Further, the polyester film is 5 to 5
Preferably, it has a thickness in the range of 0 μm. When the thickness of the polyester film is 5 μm or less, the polyester film is easily damaged during processing, pinholes and the like are generated, and the effect of preventing corrosion of the can and elution of metal may not be sufficiently obtained. Further, when the thickness is 50 μm or more, the residual stress becomes large, and the adhesion of the polyester film to the metal plate tends to decrease when a drawing process such as a neck-in process is performed on the can body.

The polyester film is heated and bonded to the metal plate for forming the can body of the can via the adhesive layer. Therefore, in order to secure dimensional stability against heat treatment, the material properties are set to 150 ° C. A biaxially stretched polyester film having a heat shrinkage in the longitudinal direction of 1.2% or less and a heat shrinkage in the width direction of 0% when held for 30 minutes is preferable. Further, in order to secure the dimensional stability, heat treatment may be performed in advance at 160 ° C. for about 6 seconds, but a thermosetting resin is particularly formed on the side opposite to the surface on which the adhesive layer is provided. Preferably, a cured overcoat layer is provided. By providing the cured overcoat layer, the residual stress of the polyester film is reduced, the expansion and contraction of the film is regulated, the dimensional stability is secured, and the scratch resistance is improved. In the case of welding cans, after filling the contents, heat sterilization (retort sterilization)
Is usually carried out, but by providing the cured overcoat layer, it is possible to prevent the low polymerization degree component (oligomer) in the polyester film from being deposited on the surface during heat treatment such as retort sterilization treatment. , Improves the slipperiness.

The thermosetting resin forming the cured overcoat layer is preferably a resin capable of forming a cured film at a high temperature and in a short time. For example, the thermosetting resin is composed of an epoxy resin and an aminoplast resin and is used as a short-time curing catalyst. Those containing an acid or an inorganic acid such as phosphoric acid or polyphosphoric acid are suitable. It is preferable that silicon or wax is added to the thermosetting resin in order to prevent oligomer precipitation and improve slipperiness.

When the polyester film is coated on the outer surface of the can of the metal plate, the polyester film may be printed to impart aesthetics to the can body or to perform a required display. In such cases, strength for printing and dimensional stability against heat treatment when bonded to the metal plate are required, so that a heat-resistant polyester film such as polyethylene naphthalate, a uniaxially or biaxially stretched polyethylene terephthalate film Are preferred.

When printing is performed on the polyester film, a printing layer made of a resin composition containing a pigment is provided between the polyester film and the adhesive layer. The printing layer may be provided between the polyester film and the overcoat layer, but by being provided between the polyester film and the adhesive layer as described above, the printing layer is formed of a polyester film. It is preferred because it is protected from trauma. When performing multicolor printing for aesthetics and required display, the printing layer is formed by laminating the resin composition one color for each color of the pigment.

When the printing layer is subjected to the retort sterilization treatment after forming the welding can body and filling the contents, a whitened portion may be formed and printing may become unclear. Therefore,
In order to prevent whitening due to the retort sterilization treatment, a size coat layer made of a resin composition obtained by removing the pigment from the resin composition forming the print layer is provided between the print layer and the adhesive layer. .

The resin composition for forming the printing layer forms an adhesive layer by heating at a high temperature for a short time to obtain a sufficient adhesive strength between the can and the metal plate for forming the can body. It is preferable that the resin is selectively used depending on the type of the resin. That is, when the adhesive layer is a resin containing the epoxy resin having the average molecular weight and the acid anhydride-based curing agent at the above-mentioned weight ratio, the resin composition forming the printing layer includes an epoxy butyral-based resin and a polyisocyanate. A resin composition composed of a base resin and containing a pigment or a resin composition composed of a polyester polyurethane resin and a polyisocyanate resin and containing a pigment is suitable.

The resin forming the adhesive layer preferably contains an inorganic or organic pigment for hiding the base of the metal plate, and titanium oxide is particularly preferred as the pigment. The titanium oxide has a weight ratio of 2 to the resin.
It is used in the range of 0/80 to 80/20.

When the polyester film covers the inner surface side of the can of the metal plate, it may be plain, and there is no need for a cured overcoat layer and printing. In this case,
Since the strength, dimensional stability and the like are not strictly required, the polyester film may be a non-stretched polyester film, or may be a uniaxially or biaxially stretched polyester film. Polyethylene terephthalate film is suitable from the viewpoint of can quality when it becomes a body.

The polyester film for covering a can body material provided with the adhesive layer, the printing layer and the cured overcoat layer is prepared by applying a thermosetting resin to one surface of the polyester film and drying the cured overcoat. An overcoat layer forming step of forming a layer, a printing step of applying a resin composition containing a pigment to the other surface of the polyester film, and drying to form a printed layer, and forming a printed layer on the surface on which the printed layer is provided. An epoxy resin having a number average molecular weight of 5,000 to 20,000 and an acid anhydride-based curing agent in a ratio of 70/30 to 99/1.
An adhesive layer forming step of applying and drying a thermosetting resin-based adhesive composed of a resin containing at a weight ratio of: and forming the thermosetting resin-based adhesive layer is advantageously performed by the manufacturing method. Can be.

Either the overcoat layer forming step or the printing step may be performed first, but from the viewpoint of ensuring dimensional stability, the overcoat layer forming step is performed prior to the printing step.

When the size coat layer is formed between the printing layer and the adhesive layer, the manufacturing method includes the step of removing the pigment from the resin composition forming the printing layer following the printing step. A size coat layer forming step of forming a size coat layer by applying and drying the composition.

In the above-mentioned manufacturing method, the formation of each of the overcoat layer, the print layer, the size coat layer and the adhesive layer is performed by gravure printing or coating.

[0030]

The polyester film for coating a can body material of the present invention has a number average molecular weight of 5,000 to 20,000 on one surface.
Of epoxy resin and acid anhydride-based curing agent at 70 / 30-9
Since an adhesive layer made of a resin containing the resin in a weight ratio of 9/1 is provided, when the adhesive is heated at a high temperature when it is heated and adhered to the metal plate for forming the can body of the can body, the curing agent causes the adhesive The curing of the layer is accelerated, and a strong adhesive force can be obtained in a short time.

The polyester film for covering a can body material of the present invention has a cured overcoat layer made of a thermosetting resin provided on the side opposite to the surface on which the adhesive layer is provided, so that the When the polyester film is heat-bonded to the metal plate for forming the can body via the adhesive layer, the residual stress of the polyester film is reduced and expansion and contraction are regulated, so that dimensional stability against heat treatment is ensured. Further, by the cured overcoat layer, during the heating treatment such as retort sterilization treatment after filling the contents of the can body, precipitation of oligomers in the polyester film on the can surface, scratches on the film surface are prevented, and Slipperiness is improved.

In the polyester film for coating a can body material of the present invention, a printing layer made of a resin composition containing a pigment is provided between the polyester film and the adhesive layer, and is adhered by heating to the metal plate. Thereby, it is possible to impart aesthetics to the can body or perform a required display without depending on the coating printing. When the printing layer is provided, further, between the printing layer and the adhesive layer, by providing a size coat layer made of a resin composition obtained by removing the pigment from the resin composition forming the printing layer During the retort sterilization treatment after filling the contents in the can body, whitening of the printing layer is prevented, and the printing layer becomes clear.

As the printing ink used for forming the printing layer, conventionally known printing inks can be used. Examples of resin components include polyurethane resin, polyester polyurethane resin, epoxy resin, epoxy butyral resin, vinyl resin, and cellulose resin. And a resin composed of at least one of a polyisocyanate resin and a polyisocyanate resin.

The resin composition for forming the printing layer is a resin composition containing an epoxy butyral resin and a polyisocyanate resin and containing a pigment, or a resin composition containing a polyester polyurethane resin and a polyisocyanate resin and containing a pigment. When the polyester film is heated and adhered to the metal plate via the adhesive layer, a strong adhesive force can be obtained by heating at a high temperature for a short time, and the content can be obtained at the time of forming the can or the can. It does not peel off during retort sterilization after filling.

In the polyester film for covering a can body material of the present invention, since the adhesive layer contains titanium oxide as a pigment, the base material of the metal plate is concealed when bonded to the metal plate by heating. The film surface becomes beautiful.
In particular, when the printing layer is provided, the printing is sharpened by using the adhesive layer containing the titanium oxide as a background.

According to the method for producing a polyester film for covering a can body material of the present invention, since the overcoat layer forming step is provided, the residual stress of the polyester film is alleviated and the stretchability is regulated, so that the polyester film can be formed in a subsequent step. The resulting polyester film has improved dimensional stability against heat treatment. The dimensional stability of the polyester film is further improved by performing the overcoat layer forming step prior to the printing step.

In the method for producing a polyester film for coating a can body material according to the present invention, after the printing step, a resin composition obtained by removing the pigment from the resin composition forming the print layer is applied and dried to form a size coat layer. By providing a size coat layer forming step of forming a polyester film, a polyester film that can prevent whitening of the printed layer due to retort sterilization treatment after can-making is obtained.

In the method for producing a polyester film for covering a can body material according to the present invention, each of the overcoat layer, the print layer, the size coat layer and the adhesive layer is formed by gravure printing and coating. It is formed to an even thickness.

[0039]

Embodiment 1 Next, the present invention will be described in more detail with reference to the accompanying drawings. 1 and 2 are explanatory sectional views showing the structure of the polyester film for coating a can body material of the present invention, and FIG. 3 is a diagram for forming a can body of a can body to which the polyester film for coating a can body material of the present invention has been heated and adhered. FIG. 4 is an explanatory sectional view of a metal plate, FIG. 4 is a plan view schematically showing a configuration example of an apparatus for heating and bonding a polyester film for coating a can body material to a metal plate for forming a can body of a can body, and FIG. FIG. 14 is a side view of the transport path of the device No. 4;

In this embodiment, a polyester film 1a for coating a can body material as shown in FIG.
Is used. As shown in FIG. 1 (a), a polyester film 1a is a biaxially stretched polyethylene terephthalate having a thickness of 12 μm (hereinafter, polyethylene terephthalate is made of PET).
A transparent cured overcoat layer 3 composed of an epoxy resin and an aminoplast resin and formed of a thermosetting resin to which a phosphoric acid catalyst has been added is provided on one surface of the film 2, and an epoxy resin is provided on the opposite surface. A printing layer 4a made of a butyral resin and a polyisocyanate resin and printed with a printing ink containing a pigment is provided.
The printing layer 4a is multi-color printed in order to impart aesthetics to the outer surface of the can and to perform a required display, and is formed by laminating the printing inks containing pigments of the required colors for each color. I have.

Then, on the printing layer 4a, a bisphenol-type epoxy resin obtained by a reaction between bisphenol and epichlorohydrin, an epoxy resin having a number average molecular weight of 10,000, and glycerol tristrimellitate anhydride as a trimellitic anhydride-based curing agent. Is provided with a thermosetting resin-based adhesive containing 95/5 by weight.

As the polyester film adhered to the inner surface side of the can body forming metal plate of the can body, the polyester film 6 for covering the can body material shown in FIG. 2 is used. As shown in FIG. 2, the polyester film 6 is formed on one surface of a biaxially stretched PET film 2 having the same thickness as the polyester film 1a and having a thickness of 12 μm.
An adhesive layer 5 made of the same thermosetting resin-based adhesive is provided. The polyester film 6 is not printed and is plain, and the surface on which the adhesive layer 5 is provided has been subjected to corona discharge treatment in advance.

The polyester film 1a was manufactured as follows. First, a long biaxially stretched PET film 2 having one surface subjected to corona discharge treatment is drawn out, and a phosphoric acid catalyst made of an epoxy resin and an aminoplast resin is added to the surface not subjected to the corona discharge treatment. Solvent-based thermosetting resin was applied with a gravure roll,
The coating was dried at 60 ° C. for 8 seconds to form a cured overcoat layer 3 having a coating amount of 1.0 g / m ² , and was cooled to 50 ° C. or lower and wound up.

Next, the long biaxially stretched PET film 2 on which the cured overcoat layer 3 was formed was pulled out, and a pigment comprising an epoxy butyral resin and a polyisocyanate resin was formed on the opposite surface of the cured overcoat layer 3. Was printed with a gravure roll and dried to form a printed layer 4a. The printing layer 4a has a predetermined printing pattern for a single can body formed of a biaxially stretched PET so as to impart aesthetics to the outer surface of the can and to perform a required display.
It is formed continuously in the longitudinal direction of the film 2.

The printing layer 4a is formed so that the printing ink required for forming the printing pattern is printed for each color as described above, and the applied amount of ink is 1.0 g / m ² . After forming the printing layer 4a, the long biaxially stretched PET film 2 was cooled, wound up, and aged for 2 days to cure the printing layer 4a.

Next, the long biaxially stretched PET film 2 on which the printing layer 4a is formed is pulled out, and the epoxy resin and glycerol tristrimellitate anhydride are placed on the printing layer 4a at the above-mentioned weight ratio. The resin solution dissolved in the solvent was applied by a gravure roll at a speed of 57 m / min.
Then, at 120 ° C. so that the curing reaction of the adhesive does not progress.
Was dried for 10 seconds to form an adhesive layer 5 composed of the thermosetting resin-based adhesive having a coating amount of 2.5 g / m ^2. After cooling, the film was rolled up to obtain a polyester film 1a.

In the polyester film 1a, the cured overcoat layer 3 is formed first, and then the print layer 4a is formed, so that the print pattern can be obtained with excellent dimensional accuracy. In addition, although the adhesive layer 5 is formed last, since it has good tack-free properties when it is wound up, there is no fear that it will cause any trouble when used in the next step.

The polyester film 6 was manufactured as follows. First, a long biaxially stretched PET film 2 similar to the one used in the production of the polyester film 1a is drawn out, and one surface thereof is subjected to a corona discharge treatment. The solution was applied in the same manner as the polyester film 1a. Then, in the same manner as the polyester film 1a, the polyester film 6 is dried to form an adhesive layer 5 composed of the thermosetting resin-based adhesive of 2.5 g / m ^2. Obtained.

Next, using the polyester films 1a and 6, a welded can was manufactured. In the welded can body of this embodiment, as shown in FIG. 3, the polyester film 1a is heated and bonded to the outer surface side of the can body forming metal plate 7 of the can body via the adhesive layer 5, and the protective coating layer 9 is formed. The polyester film 6 is heat-bonded to the inner surface of the can via the adhesive layer 5 to form the protective coating layer 10. In this embodiment, the metal plate 7 has a plate thickness of 0.22 mm and a nickel amount of 70 on the surface.
mg / m ² of nickel underlayer, on which a tin amount of 0.
Equipped with a tin layer of 8 g / m ² , and the uppermost layer is 15
Using a tin-plated steel sheet further provided with a metallic chromium / chromium oxide layer of mg / m ^2, the above-mentioned heat bonding was carried out by the apparatus shown in FIGS.

In the above apparatus, first, as shown in FIG.
The strip-shaped metal plates 43 cut into a plurality of lengths of the can body blanks 42 are continuously supplied to a transport path 44.

As shown in the side view of FIG. 5, the transport path 44 is provided with a first heating means 45 such as a high-frequency heating device on the upstream side.
Is provided, and the strip-shaped metal plate 43 supplied to the transport path 44 is provided.
Is heated to 170 ° C. Further, a printing film supply means 46 for supplying the long polyester film 1a printed as described above to the conveyance path 44 is provided below the conveyance path 44, and the plain and long printing film supply means 46 is provided above. A plain film supply means 47 for supplying the can inner surface coating film 6 to the transport path 44 is provided. Polyester films 1a, 6 produced as described above
Are wound up after production, and each is supplied with film supply means 4
6, 47 are provided.

The polyester films 1a and 6 are supplied to the transport path 44 by supply means 46 and 47, respectively, so as to contact the strip-shaped metal plate 43 on the side of the adhesive layer 5;
By a pressure roll 48 provided in the middle of the transport path 44,
The strip-shaped metal plate 43 heated as described above is pressure-bonded to both sides of the metal plate 43 except for the side edges 49, 49, and is temporarily bonded via the adhesive layer 5. At this time, even when the polyester film 1a is wound around the supply means 46 as described above, the films do not stick to each other because the adhesive has good blocking resistance, and the cured overcoat layer 3 is further formed. As a result, the sliding property and the scratch resistance are good, and the sheet can be properly drawn from the supply means 46 and supplied to the transport path 44.

Since the polyester films 1a and 6 are both long, the strip-shaped metal plate 43 is sandwiched between the temporarily bonded polyester films 1a and 6 and a plurality thereof are connected in a long shape. Then, the strip-shaped metal plates 43 connected in a long shape are cut one by one by first cutting means 50 such as a knife cylinder provided at the end of the transport path 44.

Next, the strip-shaped metal plate 43 to which the polyester films 1a and 6 are temporarily bonded is discharged from the transport path 44 and supplied to a second heating means 51 such as a heating oven shown in FIG. The thermosetting resin-based adhesive of the adhesive layer 5 is cured by maintaining the temperature at 215 ° C. for 1 minute in the inside 51.
As a result, the polyester films 1a and 6 are completely adhered to the strip-shaped metal plate 43, and a strong adhesive force is obtained.

As described above, the polyester film 1
The strip-shaped metal plate 43 to which a and 6 are adhered is then cooled in a cooling unit 52, and then supplied to a second cutting unit 53 such as a slitter, and cut into single can body blanks 42. Since the cured overcoat layer 3 is formed on the polyester film 1a as described above, the dimensional accuracy of the original printing can be maintained even by heating during the temporary bonding or heating in the heating oven 51. it can.
Therefore, the can body blank 42 can be cut in accordance with the print pattern of the print layer 4a accurately.

Next, the can body blank 42 obtained as described above is connected to the printed polyester film 1a.
The side with the adhesive bonded is rounded with the outer side of the can, and both side edges 49
Were overlapped and welded together, and the welded joint on the inner surface side of the can not covered with the polyester film 6 was covered and corrected using an epoxyphenol resin-based correction paint to form a can body. Next, a neck-in process was applied to both ends of the can body, and an easy-open can lid having one end coated with an epoxy phenol resin on the inner surface side was double-tightened to produce a welded can body.

In the welded can, the adhesion of the polyester films 1a and 6 to the metal plate 7 was observed, and the enamel value of the can was measured to determine the presence or absence of a metal exposed portion. Table 1 shows the results.

Next, the welded can body is filled with coffee as a content, and a can lid having a polyester film coated on the inner side of the can at the open end of the welded can body is double-tightened to sterilize by heating. Processing (retort sterilization) to produce a can, and the polyester film 1a after the retort sterilization
Was observed. In addition, the cans were stored at 37 ° C. for 6 months and opened, and the amount of iron eluted from the contents was measured. Table 1 shows the results.

[0059]

Embodiment 2 In this embodiment, the weight of the epoxy resin of the thermosetting resin-based adhesive forming the adhesive layer 5 and glycerol tristrimellitate anhydride in the polyester film 1a shown in FIG. The polyester films 1a and 6 were heat-bonded to the metal plate 7 in the same manner as in Example 1 except that the ratio was 90/10.

Next, a can body was manufactured from the can body blank 42 in the same manner as in Example 1, the adhesion of the polyester films 1a and 6 to the tin-plated steel sheet was observed, and the enamel value of the can body was measured. The measurement was performed to determine the presence or absence of a metal exposed portion. Table 1 shows the results.

Next, the can body was filled with coffee as a content, and a can lid having a polyester film coated on the inner surface side of the can at the open end of the welded can body was double-tightened to perform a retort sterilization treatment. Was performed to produce a can, and the appearance of the polyester film 1a after the retort sterilization treatment was observed. In the present embodiment, in the thermosetting resin-based adhesive forming the adhesive layer 5, the blending ratio of the trimellitic anhydride-based curing agent (glycerol tristrimellitate anhydride) was determined according to the first embodiment.
Since it is larger than that, the whitening of the printing layer 4a in the retort sterilization treatment was prevented, and the printing was maintained in a clear state. In addition, the cans were stored at 37 ° C. for 6 months and opened, and the amount of iron eluted from the contents was measured. Table 1 shows the results
Shown in

[0062]

Embodiment 3 In this embodiment, in the polyester film 1a shown in FIG. 1A, the thermosetting resin-based adhesive forming the adhesive layer 5 contains 60% by weight of a white pigment of titanium oxide. Except that, the polyester films 1a and 6 were heat-bonded to the metal plate 7 in the same manner as in Example 1.

Next, a can body was manufactured from the can body blank 42 in the same manner as in Example 1, the adhesion of the polyester films 1a and 6 to the tin-plated steel plate was observed, and the enamel value of the can body was measured. The measurement was performed to determine the presence or absence of a metal exposed portion. Table 1 shows the results.

Next, the can body is filled with coffee as a content, and a can lid having a polyester film coated on the inner surface side of the can at the open end of the weld can body is double-tightened to perform a retort sterilization treatment. Was performed to produce a can, and the appearance of the polyester film 1a after the retort sterilization treatment was observed. In this example, since the adhesive layer 5 contained a white pigment, the base of the metal plate 7 was concealed, and the printing of the printing layer 4a became clear. In addition, the cans were stored at 37 ° C. for 6 months and opened, and the amount of iron eluted from the contents was measured. Table 1 shows the results.

[0065]

[Embodiment 4] In this embodiment, the can body blank 4 of Embodiment 1 is used.
In the can body formed from 2 above, the coating correction of the welded joint on the inner surface side of the can not covered with the polyester film 6 is replaced with the epoxy phenol resin correction paint of Example 1 and a thermoplastic polyester resin powder paint A can body was manufactured in the same manner as in Example 1 except that a coating film having an average film thickness of 30 μm was formed by performing a heat treatment at 250 ° C. for 6 seconds after coating. And
Polyester film 1a for the tin-plated steel sheet,
While observing the adhesiveness of No. 6, the enamel value of the can was measured to determine the presence or absence of a metal exposed portion.
Table 1 shows the results.

Next, the can body is filled with coffee as a content, and a can lid having a polyester film coated on the inner side of the can at the open end of the weld can body is double-tightened to perform a retort sterilization treatment. Was performed to produce a can, and the appearance of the polyester film 1a after the retort sterilization treatment was observed. In addition, the cans were stored at 37 ° C. for 6 months and opened, and the amount of iron eluted from the contents was measured. Table 1 shows the results.

According to the can body obtained in this embodiment, since the thermoplastic polyester resin powder coating is used as the coating for coating the welded joint of the can body, the entire inner surface of the can body is made of polyester. It can be coated with a resin, and the flavor of the contents can be improved. Further, in this embodiment, the easy-open can lid coated with the epoxy phenol resin on the inner surface side is double-tightened as in the first embodiment, but the easy-open can lid coated with a polyester film on the inner surface side is used. By doing so, the entire inner surface side of the can body can be covered with the polyester resin,
The flavor of the contents can be further improved.

[0068]

Embodiment 5 In this embodiment, a metal plate 7 is formed in the same manner as in Embodiment 1 except that the polyester film 1b shown in FIG. 1B is used instead of the polyester film 1a shown in FIG. The polyester films 1b and 6 were bonded by heating.

The polyester film 1b is shown in FIG.
As shown, the cured overcoat layer 3 was provided on one surface of the same PET film 2 as in Example 1 in the same manner as in Example 1, and provided on the opposite surface in the same manner as in Example 1. A size coat layer 8 made of a resin having the same composition as the printing ink of the print layer 4a and containing no pigment is provided on the print layer 4a, and an adhesive layer 5 is provided on the size coat layer 8 in the same manner as in Example 1. Have been. Polyester film 1b
Was manufactured as follows. First, a long biaxial stretch P similar to that used in the production of the polyester film 1a was used.
The cured overcoat layer 3 was formed on the ET film 2 in the same manner as in Example 1, cooled, and wound up. next,
Long biaxial stretching P on which cured overcoat layer 3 is formed
After the ET film 2 is pulled out and the printing layer 4a is formed in the same manner as in Example 1, a resin solution containing the same epoxy butyral resin and polyisocyanate resin as the printing layer 4a but containing no pigment is gravure rolled. After printing and drying, the size coat layer 8 was formed. next,
The long biaxially stretched PET film 2 on which the size coat layer 8 was formed was cooled and then wound up and aged for 2 days. Then, an adhesive layer 5 was formed on the size coat layer 8 of the long biaxially stretched PET film 2 in the same manner as in Example 1, cooled, and wound up to obtain a polyester film 1b.

Next, a can body was manufactured from the can body blank 42 in the same manner as in Example 1, the adhesion of the polyester films 1a and 6 to the tin-plated steel plate was observed, and the enamel value of the can body was measured. The measurement was performed to determine the presence or absence of a metal exposed portion. Table 1 shows the results. next,
The can body is filled with coffee as a content, and the can end is subjected to a retort sterilization treatment by double-tightening a can lid having a polyester film coated on the inner side of the can at the open end of the welded can body to produce a can. Then, the appearance of the polyester film 1a after the retort sterilization treatment was observed. In this embodiment, the printing layer 4
Since the size coat layer 8 was provided on the print layer 4a, the print layer 4a was not whitened even by the retort sterilization treatment, and the print was kept clear. In addition, the cans were stored at 37 ° C. for 6 months and opened, and the amount of iron eluted from the contents was measured. Table 1 shows the results.

[0071]

Embodiment 6 In this embodiment, the polyester film 1c shown in FIG. 1C is used in place of the polyester film 1a shown in FIG. Example ² except that a tin-plated steel sheet provided with a tin layer having a tin amount of 1.2 g / m ² and a surface thereof further provided with a metal chromium / chromium oxide layer having a chromium amount of 18 mg / m ² was further provided thereon. In the same manner as in Example 1, the polyester films 1c and 6 were heat-bonded to the tin-plated steel sheet.

The polyester film 1c is shown in FIG.
As shown, a cured overcoat layer 3 is provided on one surface of the same PET film 2 as in Example 1 in the same manner as in Example 1, and a polyurethane polyester resin and a polyisocyanate-based resin are formed on the opposite surface. A printing layer 4b printed with a printing ink containing a pigment is provided. The printing layer 4b is formed by laminating the printing ink containing the pigment of each color for each required color. The adhesive layer 5 is provided on the print layer 4b in the same manner as in the first embodiment.

The polyester film 1c was manufactured as follows. First, a long biaxially stretched PET film 2 similar to that used in the production of the polyester film 1a was used.
Then, a cured overcoat layer 3 was formed in the same manner as in Example 1, cooled, and wound up. Next, a long biaxially stretched PET film 2 having the cured overcoat layer 3 formed thereon
The printing ink containing a pigment made of a polyurethane polyester resin and a polyisocyanate resin and containing a pigment was printed on a surface opposite to the cured overcoat layer 3 by a gravure roll, and dried to form a printing layer 4b. Printing layer 4b
Prints the printing ink for each color as described above,
It is formed so that the ink application amount is 1.0 g / m ² .
After forming and cooling the printing layer 4b, a long biaxially stretched PET
Film 2 was wound up and aged for 2 days.

Next, the long biaxially stretched PET film 2 on which the print layer 4b was formed was pulled out, and a resin solution of the same thermosetting resin-based adhesive as in Example 1 was gravure rolled onto the print layer 4b. The adhesive layer 5 was formed in the same manner as in Example 1, cooled, and wound up to obtain a polyester film 1c.

Next, a can body was manufactured from the can body blank 42 in the same manner as in Example 1, and the adhesion of the polyester films 1c and 6 to the tin-plated steel sheet was observed, and the enamel value of the can body was measured. The measurement was performed to determine the presence or absence of a metal exposed portion. Table 1 shows the results.

Next, the can body was filled with lemon tea as a content, and a can lid having a polyester film coated on the inner side of the can at the open end of the welding can body was double-tightened to sterilize the retort. After the treatment, a can was manufactured, and the appearance of the polyester film 1c after the retort sterilization treatment was observed. In addition, the cans were stored at 37 ° C. for 6 months and opened,
The amount of iron eluted with respect to the contents was measured. Table 1 shows the results.

[0077]

Embodiment 7 In this embodiment, a polyester film 1c shown in FIG. 1 (c) is used instead of the polyester film 1a shown in FIG. 1 (a), and a thermosetting type in which an adhesive layer 5 is formed on the polyester film 1c. Except that the resin-based adhesive contained 60% by weight of a white pigment of titanium oxide,
In the same manner as in Example 1, the polyester films 1c and 6 were bonded to the metal plate 7 by heating.

Next, a can body was manufactured from the can body blank 42 in the same manner as in Example 1, the adhesion of the polyester films 1c and 6 to the tin-plated steel plate was observed, and the enamel value of the can body was measured. The measurement was performed to determine the presence or absence of a metal exposed portion. Table 1 shows the results.

Next, the can body is filled with coffee as a content, and a can lid having a polyester film coated on the inner side of the can at the open end of the weld can body is double-tightened to perform a retort sterilization treatment. Was carried out to produce a can, and the appearance of the polyester film 1c after the retort sterilization treatment was observed. In this example, since the adhesive layer 5 contained a white pigment, the base of the metal plate 7 was concealed, and the printing of the printing layer 4b became clear. In addition, the cans were stored at 37 ° C. for 6 months and opened, and the amount of iron eluted from the contents was measured. Table 1 shows the results.

[0080]

[Table 1]

The types of the surface-treated steel sheets described in Table 1 are as follows.

TNS is a nickel underlayer having a nickel amount of 70 mg / m ² , a tin layer having a tin amount of 0.8 g / m ² on the underlayer, and a metal layer having a chromium amount of 15 mg / m ^{2 on} the uppermost layer. It means a tin-plated steel sheet provided with a chromium / chromium oxide layer. LTS means a tin-plated steel sheet provided with a tin layer having a tin amount of 1.2 g / m ² and a metal chromium / chromium oxide layer having a chromium amount of 18 mg / m ^{2 on} the tin layer.

The curing agent in the adhesive section means glycerol tristrimellitate anhydride, and ERV is an abbreviation for enamel value.

From Table 1, it is clear that the polyester film for coating the can body material of the present invention is firmly adhered to the metal plate for forming the can body of the can body by heating at a high temperature for a short time. It is clear from the measured values that there is no exposed metal portion on the metal plate to which the polyester film is adhered.

As shown in Table 1, according to the polyester film for coating a can body material of the present invention, no abnormality such as whitening was observed in the appearance even after the retort sterilization treatment, and the printing was clear. It is clear that the whitening prevention effect is particularly remarkable when the size coat layer 8 is provided (Example 5). Further, when the adhesive layer 5 contains a white pigment of titanium oxide (Examples 3 and 7), the white adhesive layer 5 conceals the base of the metal plate 7, so that the printing becomes clearer. Become.

Further, from Table 1, according to the polyester film for coating the can body material of the present invention, the amount of iron eluted to the contents is extremely small, and the adhesive strength is maintained even after long-term storage. It is clear that corrosion of the metal plate for forming the body and change in the flavor of the contents can be prevented.

Further, from Table 1, it is apparent that the polyester film for coating the can body material of the present invention is firmly bonded irrespective of the type of metal plate for forming the can body of the can body.

[0088]

As is apparent from the above, according to the polyester film for coating a can body material of the present invention, an epoxy resin having a number average molecular weight of 5,000 to 20,000 and an acid anhydride curing agent are provided on one surface. Is provided in a weight ratio of 70/30 to 99/1, so that the adhesive layer has good blocking resistance, and is further bonded to a metal plate for forming a can body of a can body. A strong adhesive force can be obtained by heating at a high temperature for a short time when bonding is performed via the agent layer. Since the polyester film for coating a can body material of the present invention is provided with a cured overcoat layer made of a thermosetting resin on the side opposite to the surface on which the adhesive layer is provided, the heat treatment at the time of the heat bonding is performed. In addition to being excellent in dimensional stability, precipitation of oligomers can be prevented, and scratch resistance and slipperiness of can materials and can bodies are improved.

The polyester film for covering a can body material of the present invention is provided with a printing layer made of a resin composition containing a pigment between the polyester film and the adhesive layer, and is adhered by heating to the metal plate. Thus, it is possible to impart aesthetics to the can body or perform a required display without depending on the painting. When the printing layer is provided, further,
Between the printing layer and the adhesive layer, by providing a size coat layer made of a resin composition obtained by removing the pigment from the resin composition forming the print layer, the can was filled with the contents. During the retort sterilization treatment, whitening of the printing layer can be prevented, and the sharpness of the printing layer can be maintained.

In the polyester film for covering a can body material of the present invention, the resin composition forming the printing layer is a resin composition containing an epoxy butyral resin and a polyisocyanate resin and containing a pigment, or a polyester polyurethane resin and a polyisocyanate. By using a resin composition comprising a base resin and containing a pigment, a strong adhesive force can be obtained between the polyester film and the metal plate by heating at a high temperature for a short time.

In the polyester film for covering a can body material of the present invention, the base material of the metal plate is concealed when the adhesive layer is heated and bonded to the metal plate by including titanium oxide as a pigment. The film surface becomes beautiful.
In particular, when the printing layer is provided, the printing can be further sharpened by using the adhesive layer containing the titanium oxide as a background.

According to the method for producing a polyester film for coating a can body material of the present invention, since the overcoat layer forming step is provided, it is possible to obtain a polyester film having excellent dimensional stability against heat treatment in a subsequent step. it can. The dimensional stability of the polyester film can be further improved by performing the overcoat layer forming step prior to the printing step.

[Brief description of the drawings]

FIG. 1 is an explanatory sectional view showing a configuration of a polyester film for coating a can body material of the present invention.

FIG. 2 is an explanatory sectional view showing the structure of a polyester film for coating a can body material of the present invention.

FIG. 3 is an explanatory cross-sectional view of a metal plate for forming a can body of a can body to which a polyester film for coating a can body material according to the present invention is adhered by heating.

FIG. 4 is a plan view schematically showing a configuration example of an apparatus for heating and bonding the polyester film for coating a can body material of the present invention to a metal plate for forming a can body of a can body.

FIG. 5 is a side view of a transport path of the apparatus of FIG.

[Explanation of symbols]

2: polyester film, 4a, 4b: printing ink, 5: thermosetting resin-based adhesive, 6: polyester film, 7: metal plate for forming a can body of a can body, 8: size coat layer, 9, 10 ... protection Coating layer.

──────────────────────────────────────────────────続 き Continuing on the front page (72) Inventor Yasuo Homma 839-1 Shimuro, Iwatsuki-shi, Saitama Prefecture Hokkai Seikan Co., Ltd. (72) Inventor Koji Matsushima 839-1 Shimuro, Iwatsuki-shi, Saitama (56) References JP-A-5-32256 (JP, A) JP-A-62-30176 (JP, A) JP-A-4-91949 (JP, A) (58) Field (Int.Cl. ⁷ , DB name) B32B 1/00-35/00

Claims (12)

(57) [Claims] 1. A polyester film which is heat-bonded to a metal plate for forming a can body of a can body via a thermosetting resin-based adhesive to form a protective coating layer, wherein a number of An epoxy resin having an average molecular weight of 5,000 to 20,000 and an acid anhydride-based curing agent are mixed in an amount of 70/30 to 99/1.
1. A polyester film for covering a can body material, comprising an adhesive layer made of a resin containing the resin film in a weight ratio of: 2. The polyester film for covering a can body material according to claim 1, wherein the acid anhydride-based curing agent is a trimellitic anhydride-based curing agent. 3. The can body according to claim 1, wherein a cured overcoat layer made of a thermosetting resin is provided on a side of the polyester film opposite to a surface on which the adhesive layer is provided. Polyester film for material coating. 4. The polyester film for coating a can body material according to claim 1, wherein a printed layer made of a resin composition containing a pigment is provided between said polyester film and said adhesive layer. 5. A size coat layer comprising a resin composition obtained by removing a pigment from a resin composition forming the print layer, is provided between the print layer and the adhesive layer. The polyester film for covering a can body material according to claim 4. 6. The polyester film for coating a can body material according to claim 4, wherein the resin composition forming the printing layer comprises an epoxy butyral resin and a polyisocyanate resin and contains a pigment. 7. The polyester film for covering a can body material according to claim 4, wherein the resin composition forming the printing layer comprises a pigment comprising a polyester polyurethane resin and a polyisocyanate resin. 8. The polyester film according to claim 1, wherein the adhesive layer contains titanium oxide as a pigment. 9. A protective coating layer is formed by heating and bonding to a metal plate for forming a can body of a can body via a thermosetting resin-based adhesive .
A method for producing a polyester film for coating a can body material, comprising: applying a thermosetting resin to one surface of the polyester film and drying to form a cured overcoat layer; A printing step of applying and drying a resin composition containing a pigment on the other surface of the film to form a printed layer; and providing a number-average molecular weight of 5,000 on the surface on which the printed layer is provided.
~ 20,000 epoxy resin and acid anhydride curing agent
Thermosetting made of resin containing 0/30 to 99/1 by weight
Applying and drying a mold resin adhesive, the thermosetting resin
A method for producing a polyester film for covering a can body material, comprising: an adhesive layer forming step of forming a system adhesive layer . 10. The method for producing a polyester film for covering a can body material according to claim 9 , wherein the step of forming the overcoat layer is performed prior to the printing step. 11. Following the printing step, applying a resin composition obtained by removing a pigment from the resin composition forming the print layer,
The method for producing a polyester film for coating a can body material according to claim 9, further comprising a size coat layer forming step of forming a size coat layer by drying. 12. The method of claim 11, wherein the overcoat layer, printed layer, the formation of each layer of the size coat layer and adhesive layer, also claim 9, characterized in that both gravure printing, by coating
A method for producing a polyester film for coating a can body material according to claim 11 .